Process for the introduction of rare earths in addition alloys



United States Patent PROCESS FOR THE INTRODUCTION OF RARE EARTHS IN ADDITION ALLOYS Jiirgen Motz, Frankfurt am Main, and Franz Kaess and Erwin Vogel, Trostberg, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany, and Suddeutsche Kalkstickstotf-Werke Aktiengesellschaft, Trostherg, Germany No Drawing. Application June 10, 1957 Serial No. 664,491

Claims priority, application Germany June 26, 1956 6 Claims. (Cl. 75-2'7) Rare earths-metals and alloys, in particular cerium, are used to a wide extent in the iron and steel industry; on the one hand, they are frequently employed as alloying constituents in the steel industry and, on the other hand, additions of rare earths in pureor alloyed form to cast iron produce globular graphite formation, resulting in a high-grade product. It is also known that rare earths, particularly cerium, can counteract the disturbing effect of certain elements (titanium, lead, tin and so forth) on the formation of globular graphite in cast iron produced by the magnesium process. To attain this, small quantities of rare earths are frequently added to the ordinary magnesium alloys.

When employed for this purpose, the metals of the rare earths are added, preferably in the form of so-called cerium mischmetall, either directly to the iron melts or they are components of addition alloys, in particular silicon-based alloys, and are introduced together with other material, such as silicon, alkaline earth metal, manganese and aluminum. Such alloys were hitherto produced by alloying the hardener melts with metals of the rear earths, preferably in the form of mischmetall.

The invention related to a process for the production of hardeners or addition alloys based on silicon, which contain rare earths and are intended for the treatment of iron and steel melts, and it consists in that the rare earths are added to the hardeners or to the materials from which they are produced, in the form of substances containing oxygen or in the form of their salts, instead of in metallic form. The oxides, salts, ores or ore concentrates of the rare earths, such as ceric earths or monazite sand, are then reduced by the hardener smelting or during their production. The reduction is effected by silicon and/ or base alloy components of silicon based alloys, such as magnesium or calcium in such quantities that, in solid state, they are intermetallicly bonded with the silicon. The presence of these electronegative metals is, however, by no means necessary. The alloy smelting can equally well be alloyed with higher grade elements such as iron and/ or manganese and contain in addition chromium or nickel as well as small quantities of the usual accompanying elements. The oxides or salts of rare earths may, however, also be reduced during the production of such alloys, for example when ferrosilicon, silicornanganese or calcium silicon are produced, for example by adding oxides or salts of the rare earths to the formation mixture of ferrosilicon which consists of sand, coal and iron scrap. These results are unexpected seeing that it was not to be anticipated that the base rare earths can be reduced by alloys based on silicon which are in addition alloyed with more electropositive components such as iron and/or manganese.

The following examples serve for explaining the invention more clearly:

2,926,080 Patented Feb. 23, 1960 2 Example 1 Ferrosilicon alloys containing 98%, 90%, or

20% silicon were smelted down in'a carbon resistent furnace with 2.5% cerium-lanthanium mixed oxides containing 78.7% Ce'+La or with 2% monazite sand containing 48.1% Ce-l-La and heated to temperatures of 1500 C. and higher. After pouring off, the contents of rare earths in the alloys were ascertained. The analysis figures in the following table show that the oxides and the phosphates respectively were considerably reduced in the case'of the melts with a high silicon content.

' Ce+La, found Yield, Alloy added 1 percent Ce+La, percent j percent 2% monazitel. 0. c (163 66 2.5% oxide 1. 98 l. 23 62 2.5% OXidL 1. 98 x 0. 94 47 2% monazite 0.96 0. 1 10 Example 2 In another sphere technical silicon (981% Si) was melted anelectric arc furnace with a carbon electrode in a carbon crucible with a high-basic lime-fluorite slag. Mixed oxides of the rare earths (78.7% Ce+La) were added to the'slag in quantities amounting to 40%, of the Si-charge. 1 Tests showed in the finished alloy 2%' Ca and 28.6% Ce+La, which means that 91% of the rare earths added in the form of oxide had been reduced. The tests also proved that, according to this process, high cerium contents can be introduced into silicon. alloys and that their reduction takes place to a great extent before that of the calcium.

Example 3 For the purpose of obtaining other addition alloys, calcium silicon (32% Ca) was melted down with 12% cerite earths. In this way the calcium silicon received 2. 1% cerium.

Example 4 Mg, Ca, Fe, Ce, La, Si percent percent percent percent percent 29. 4 5. 1 6. 2 0. 28 0. 20 Remainder.

To enable this alloy to be compared with an alloy free from cerium and an alloy containing cerium into which this material was introduced according to the conventional method, two additional alloys were melted which were made up from the same quantities of magnesium, calcium silicon and ferrosilicon. The first of the two alloys con-' tained no further additions. To the second 1% of cerium mixed metal with a cerium content of 45% was added. The following contents were found in the alloys:

Mg, Ca, Fe, Ce, La, Si percent percent percent percent percent 31.0 4. 9 6. 0 Remainder.

28. 2 5. 5 5. 8 0. 32 0. 25 Remainder.

With the addition alloy, to which no rare earths were added in any form, only 50% of the free graphite was formed in nodules in the cast iron containing 0.11% titanium. On the other hand, by the addition of the key alloys in which rare earths were introduced by the conventional method and the method according to the invention, a formation of more than 90% spherulites could be obtained in the same iron;

In the cases when monazite sand is introduced as carrier of the rare earths, the phosphates are reduced during the reaction into phosphides. These hydrolyse, especially when stored in moist air, liberating hydrogen phosphides and, in the case of higher concentrations, can reduce the storage stability of the alloy. If this decomposition becomes more apparent, the addition of other substances containing cerium, for example oxides or cerite earths, should be given perference to the addition of phosphates.

A particular advantage of the invention is that, instead of the expensive cerium mischmetall or other metals of the rare earths, cheap raw products of the rare earths can be used as admixture material for the addition alloys.

Needless to say it is also possible, instead of adding the rare earths to the hardeners in the form of oxides or salts, to produce them with similar substances as sinter or pressed cakes and to allow the reduction to take place by the smelting heat on the introduction of these cakes into the iron or steel baths.

We claim:

1. A process for the introduction of rare earths into silicon base alloys to produce silicon base molten alloys containing metallic rare earths suitable for the treatment of iron and steel metals which comprises treating the rare earths in the form of compounds selected from the group 4 consisting of rare earth salts and rare earth oxides with the fused components of the silicon base alloy.

2. The process of claim 1 in which said silicon base metal alloys contain magnesium.

3. The process of claim 1 in which said silicon base metal alloys contain calcium.

4. The process of claim 1 in which said silicon base metal alloys contain magnesium, calcium and iron.

5. The process of claim 1 in which said silicon base metal alloys contain iron.

6. The process of claim 1 in which the rare earth compounds are added to the raw materials from which the silican base alloys are formed before production of said silicon base alloys.

References Cited in the file of this patent UNITED STATES PATENTS 2,144,200 Rohn et a1 Jan. 17, 1939 2,771,359 Morana Nov. 20, 1956 2,794,731 Iwase et al June 4, 1957 FOREIGN PATENTS 3,089 Great Britain Oct. 11, 1906 568,315 Great Britain Mar. 29, 1945 612,607 Great Britain Nov. 16, 1948 OTHER REFERENCES Reduction by Means of Silicon, Kahlenberg and Trautmann. Paper presented at the 39th General Meeting of the American Electrochemical Society, Atlantic City, April 23, 1921. 

1. A PROCESS FOR THE INTRODUCTION OF RARE EARTHS INTO SILICON BASE ALLOYS TO PRODUCE SILICON BASE MOLTEN ALLOYS CONTAINING METALLIC RARE EARTHS SUITABLE FOR THE TREATMENT OF IRON AND STEEL METALS WHICH COMPRISES TREATING THE RARE EARTHS IN THE FORM OF COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF RARE EARTH SALTS AND RARE EARTH OXIDES WITH THE FUSED COMPONENTS OF THE SILICON BASE ALLOY. 